This application is a continuation of application Ser. No. 06/398,841, filed Jul. 16, 1982, now abandoned, which in turn is a continuation-in-part of my copending application Ser. No. 205,638 filed Nov. 10, 1980 which is a continuation of my application Ser. No. 959,303 filed Nov. 9, 1978, now abandoned.
My invention relates to electrophotographic copiers and, more particularly, to variable magnification electrophotographic copiers using movable focusing means.
In electrophotographic copiers of the prior art movable focusing means are used to vary the magnification of the light image focused upon a photoconductive surface. However, the focusing means is translated along its optical axis, in a same manner as the lens of a camera. To produce this translational movement of the focusing means is mechanically complex and expensive in view of the precision with which it must be accomplished to achieve accurate focus at various magnifications. In my invention, variable magnification is obtained by rotating the focusing means about an axis orthogonal to its optical axis, resulting in a mechanically simpler, more accurate, and less expensive construction.
The problem of changing magnification in an electrophotographic copier is particularly difficult in copiers having focusing means of fixed focal length. In such copiers a change of magnification requires not only a change in the ratio of the object distance to the image distance but also a change in the sum of the object and image distances.